Compact trace element sensor which utilizes microwave generated plasma and which is portable by an individual

ABSTRACT

A method and portable apparatus for self-powered, sensitive analysis of solid, liquid or gas samples for the presence of elements is provided. The apparatus includes a compact sensor system which utilizes a microwave power source and a shorted waveguide to induce a plasma. The microwave power source may be a magnetron or the like. The device includes a portable power supply and preferably includes a portable battery charger. The portable power supply includes a compact generator-internal combustion engine unit. The device can be operated by directly using power from the portable power supply or in a more compact embodiment by using power from batteries that are recharged by a separate portable power supply module. Pulsed microwave operation can be used to reduce average power requirements and facilitate the use of very compact units using batteries. The device is capable of being transported to and from remote sites for analysis by an individual without the need for heavy transportation equipment. A computer may be utilized to control the portable power supply, the battery charger and the microwave power source. The method and apparatus are capable of analyzing samples for the presence of several elements simultaneously using fiber optic guides and a spectrometer system. The apparatus can be contained in a plurality of readily detactable modules to facilitate transportation and field operation.

This application claims the benefit of priority of and is a continuationof U.S. patent application Ser. No. 08/552,677, now U.S. Pat. No.5,825,485, filed Nov. 3, 1995.

TECHNICAL FIELD

The present invention generally relates to methods and apparatus foranalyzing solids, liquids and gases for the presence of several traceelements simultaneously and more particularly to methods and apparatusfor analyzing solids, liquids and gases for several valuable orhazardous trace elements simultaneously using compact, portable traceelement sensor devices which are portable by an individual.

BACKGROUND OF THE INVENTION

For various undertakings such as prospecting and mining operations,national security searches for dangerous materials, and assessments ofenvironmentally harmful substances, it is necessary to analyze solids,liquids and gases to detect the presence of valuable or hazardouselements. It is desirable to utilize a sensor device which would becapable of sensitive, real time elemental analysis to monitor or detectthe presence of such elements. It is also desirable that such a sensordevice be self-powered and sufficiently compact so as to be portable byan individual. In particular, a portable sensor device would facilitateelemental analysis at particular locations, thereby eliminating the needfor special sample preparation and the necessity for sending samples tospecially equipped laboratories. It is desired that such a sensingdevice be able to readily detect the presence of valuable elements suchas gold, silver, palladium, platinum, and others. It is also desirablethat such a device be able to readily detect the presence of hazardouselements such as trace metals including lead, mercury, arsenic,beryllium, chromium, antimony, barium, cadmium, thallium, nickel andselenium. Such a device should have high sensitivity to facilitatediscovery of valuable mineral deposits. The device should also requireminimal sample preparation to be effective in the field. Such a deviceshould also be capable of detecting the presence of many differentelements simultaneously.

Instrumentation and devices for the sensitive elemental analysis ofmaterials developed to date suffer from limitations of their not beingcompact, portable devices, or being severely limited in terms of therange of elements and forms of matter that can be sampled. The use ofplasma sources for elemental excitation or detection is currently theprimary means for sensitive detection of trace elements in solids,liquids and gases. M. W. Blades et al., Application of Weakly IonizedPlasmas for Materials Sampling and Analysis, IEEE Trans. on Plasma Sci.,Vol. 19, pp. 1090-1113 (1991) have reviewed such technology, whichincluded conductively coupled plasmas, microwave-induced plasmas, andother techniques. None of the techniques so described are applicable tosensitive, real time measurements for use in a portable sensor device.Fast Fourier transform spectroscopy, as, described by J. Demirgian,Continuous Monitor for Incinerators, U.S. Department of EnergyInformation Exchange Meeting on the Characterization, Monitoring, andSensor Technologies, Dallas, Tex. (Jun. 3-4, 1992) can be used forcontinuous, near real time monitoring of molecular gases, but is notcapable of the detection of metals, especially if the metals are inparticulate form. Commercial in situ detectors, such as the BacharachInstrument Company mercury sniffer model MV-2J-W and the PacificNorthwest Laboratory Halo-sniff spectrochemical emission sensor cannotbe used as portable units for real time measurements of metals in a widerange of particulate as well as vapor form.

F. C. Fehsenfeld et al., Microwave Discharge Cavities Operating at 2450MHz, Rev. of Sci. Instrm., Vol. 36, pp. 294-298 (1965) described anumber of microwave-induced plasma (MIP) resonator cavity structures.One such structure had a built in taper to reduce its height to increasethe electric field strength for plasma breakdown. This device was aresonator, not a shorted waveguide. It also included a number offeatures that limited maximum microwave power, such as a cableconnection to the source of such power. None of the devices described byFehsenfeld are suitable for a portable sensor device.

R. M. Barnes, et al., Design Concepts for Strip-Line MicrowaveSpectrochemical Sources, Anal. Chem., Vol. 62, pp. 2650-2654 (1990)described a shorted strip-line microwave MIP arrangement with adielectric tube through the device one-quarter wavelength from theshorted end. Again, the features of this device, such as the presence ofthe strip-line and the cable connection to the source, would limit themaximum power operation of this device. The power limit would preventuse in the high power mode which may be desirable for spectroscopicanalysis of particulates and would be desirable for a portable device.

H. Matusiewicz, A Novel Microwave Plasma Cavity Assembly for AtomicEmission Spectrometry, Spectrachimica Acta, Vol. 47B, pp. 1221-1227(1992); Y. Okamoto, Annular-Shaped Microwave-Induced Nitrogen Plasma atAtmospheric Pressure for Emission Spectrometry of Solutions, AnalyticalScience, Vol. 7, pp. 283-288 (1991); and D. K. Smith, et al., MicrowaveAtmospheric Pressure Plasma Torch, Characteristics and Application, 27thMicrowave Symposium, Washington, D.C. (Aug. 2-5, 1992) described sigherpower MIP devices connected to the microwave source directly by thewaveguide. These devices are unsuitable for use in portable devices.

Other microwave-induced plasma-atomic emission spectroscopy devices aredescribed by K. A. Forbes et al., Comparison of Microwave-Induced PlasmaSources, J. of Analytical Atomic Spectrometry, Vol. 6, pp. 57-71 (1991);J. P. Matousek, Microwave-Induced Plasmas: Implementation andApplication, Prog. Analyt. Atom. Spectrosc., Vol. 7, pp. 275-314 (1984);S. R. Goode et al., A Review of Instrumentation Used to GenerateMicrowave-Induced Plasmas, Applied Spectrosc., Vol. 38, pp. 755-763(1984); and Zander et al., Microwave-Supported Discharges, AppliedSpectrosc., Vol. 35, pp. 357-371 (1981).

It would therefore be desirable to provide methods and apparatus foranalyzing solid, liquid and gas samples utilizing a self-poweredportable, sensitive trace element sensor device. It would also bedesirable to provide a compact, portable sensor device which is capableof characterizing samples containing more than one trace elementsimultaneously, thereby overcoming the shortcomings associated with theprior art.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a compact,self-powered portable trace element sensor device.

It is another object of the invention to provide a portable traceelement sensor device which can be transported by an individual andwithout the need for heavy transportation equipment.

It is another object of the invention to provide a portable traceelement sensor device which utilizes a microwave induced plasma.

It is another object of the invention to provide a portable traceelement sensor device which is capable of utilizing a pulsed ornon-pulsed microwave source to achieve high peak powers withoutrequiring a large power supply.

It is yet another object of the invention to provide a portable traceelement sensor device which is capable of analyzing solid, liquid or gascompositions.

It is yet another object of the invention to provide a portable traceelement sensor device which is capable of analyzing solid, liquid or gascompositions for the presence of several elements simultaneously.

It is still another object of the invention to provide a portable traceelement analyzer that does not require sample pretreatment for analysisto speed and simplify field measurements.

It is still another object of the invention to provide a portable traceelement sensor device which is suitable for use in connection withprospecting.

It is still another object of the invention to provide a portable traceelement sensor device which is suitable for use in connection withmining.

It is still another object of the invention to provide a portable traceelement sensor device which is suitable for use in connection with onsite analysis of hazardous elements.

It is still another object of the invention to provide a portable traceelement sensor device which is suitable for use in conjunction withvarious national security applications such as smuggling of weaponsmaterials.

It is still another object of the invention to provide a portable traceelement sensor device which includes a portable power supply circuitusing electrical power from a compact generator-internal combustionengine system.

It is still a further object of the invention to provide a compact,portable sensor device which can be operated on batteries alone.

It is still a further object of the invention to provide a portablesensor device which includes a portable battery charger module which canbe separated from the rest of the device.

It is a further object of the invention to provide a method of analyzinga solid, liquid or gas sample for several trace elements simultaneouslyusing a portable trace element sensor device.

These and other objects of the invention are provided by a portabletrace element sensor device which utilizes sensitive, real timeelemental analysis at low cost without the necessity for special samplepreparation. Preferably, the sensor device is self-powered and issufficiently compact so as to allow transportation of the device by anindividual, thereby eliminating the need for heavy transportationequipment. Power for the device would be supplied by a generator drivenby a small internal combustion engine, or rechargeable batteries. Forexample and while not meant to be limiting, one embodiment of theinvention may employ several readily connectable modules, each modulecontaining a component or components of the device therein. The modulesare constructed in a manner to facilitate connection with another moduleor modules at or near the location of the sample to be analyzed. Eachmodule and component parts therein may weigh for example, up to about 30pounds, such that the total weight of the device is less than 100pounds. The portable device of the present invention may be taken intothe field for rapid on site measurements. The device is suitable for usein connection with prospecting, mining, on site environmental analysis,and for various national security applications.

The portable sensor device uses a plasma which is induced inside awaveguide which is penetrated by openings in the wall of the waveguidesuch that gas flows through the waveguide transverse to the direction ofthe microwave power propagation. In a preferred embodiment, the gas flowis confined within a tube formed of dielectric material which istransparent to the microwaves.

The device also includes a microwave power source such as a magnetron,radar source or the like. The microwave power source can be operated ina pulsed or non-pulsed mode to minimize average power requirements andfacilitate a relatively low weight, portable design. While not to beconstrued as limiting, the detection system preferably weighs less thana total of about 200 pounds and more preferably less than 100 pounds.The microwave power source may be connected to a portable power supplyhaving a filament and anode sections. The microwave source uses a lowvoltage, high current filament supply and a high voltage, lower currentanode supply to allow for the desired pulsed or continuous operation.

In a preferred embodiment, the unit includes a light weight batterycharging system. Compact units can be designed to operate onrechargeable batteries, thereby facilitating operation by reducing sizeand weight without the generator or internal combustion engine unit.

An exhaust pump or source of compressed gas is utilized,to establishflow of solid, liquid or gas compositions through the plasma forelemental analysis. Filter optic guides transmit the plasma light to aspectrometer system for identification by line spectra of element orelements present in the sample being analyzed. In a preferredembodiment, multiple fibers and spectrometers may be employed to monitoror detect simultaneously many elements present in a sample.

In a preferred embodiment of the invention, a portable computer controlsthe spectrometer system, monitors forward and reflected power detectorsassociated with the microwave source, displays spectra and providescompositional analysis of the sample being analyzed. It is alsopreferred that the computer control the operation of the microwavesource.

The foregoing has outlined some of the more pertinent objects of thepresent invention. These objects should be construed to be merelyillustrative of some of the more prominent features and applications ofthe invention. Many other beneficial results can be attained by applyingthe disclosed invention in a different manner of modifying the inventionas will be described. Accordingly, other objects and a fullerunderstanding of the invention may be had by referring to the followingDetailed Description of the Preferred Embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the present invention, reference is had tothe following description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 illustrates a portable microwave plasma torch element sensordevice in accordance with the present invention;

FIG. 2 illustrates a portable power supply circuit suitable for use inconjunction with the microwave plasma torch element sensor deviceillustrated in FIG. 1;

FIG. 3 shows a portable battery charger suitable for use in conjunctionwith the microwave plasma torch element sensor device illustrated inFIG. 1; and

FIG. 4 illustrates a modular arrangement in accordance with oneembodiment of the present invention.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a portable trace element sensor devicewhich is capable of sensitive, real time elemental analysis of a solid,liquid or gas sample at low cost without the need for special samplepreparation. The sensor device is self-powered and can be transported byan individual, thereby eliminating the need for heavy transportationequipment. For example and while not meant to be limiting, oneembodiment of the invention may employ several readily connectablemodules, each module containing a component or components of the devicetherein. The modules are constricted in a manner to facilitateconnection to another module or modules at or near the location of thesample to be analyzed (see e.g., FIG. 4). Each module and componentparts therein may weigh for example, up to about 30 pounds, such thatthe total weight of the device is less than 100 pounds. The modules canbe transported by an individual by hand carrying the modules, or byemploying a dolly or the like. In this manner, the portable device ofthe present invention may be taken into the field for rapid on sitemeasurements. The device is capable of being designed for use inconnection with prospecting, mining, on site elemental analysis and forvarious national security applications. The present invention alsoprovides a method for analyzing samples for the presence of traceelements using a portable trace sensor device.

As mentioned above, the compact and portable features of the presentinvention facilitate use of the device in a variety of differentapplications. For example, a miner or prospector equipped with such adevice would be more efficient in locating valuable ores. The efficiencyand cost effectiveness of gold and silver mining in shaft mines woulddramatically increase by using such a device to determine which orescontain sufficiently high amounts of gold or silver to send up the shaftto the earth's surface. In addition, a much more detailed analysis ofmines and remote sites may be undertaken utilizing the device of thepresent invention, thereby insuring that potentially valuable strikesare not surpassed. In addition, extremely compact units may use higherfrequency microwave components, e.g. greater than 2.45 GHz, resulting inmuch smaller sizes and further facilitating their use at remote sitesand the like. The sensor device is also capable of being self-powered.Alternatively, the device may be plugged into existing power sources tofurther reduce size when the unit is used within or near a building,vehicle or the like.

National security is another example of the type of application whichwould have use for the present invention. Because the device provided bythe present invention is capable of making very sensitive measurements,e.g. in one part per billion range for most elements, it would bevaluable to government enforcement agencies for monitoring dangeroussubstances and the like.

Evaluation on site for harmful pollution exemplifies yet anotherapplication for the use of the device provided by the present invention.The portable device of the present invention may be employed tofacilitate the characterization of waste sites, analyze water sourcesfor pollution, and monitor industrial sites for hazardous emissions. Thedevice of the present invention thus provides a valuable tool for anyindustry, community, or groups and other entities concerned with theenvironment.

Referring now to FIG. 1, a portable microwave plasma torch elementsensor device 10 in accordance with the present invention isillustrated. While not to be construed as limiting, it is expected thata portable trace element sensor device in accordance with the presentinvention will weigh approximately 50-200 pounds and preferably lessthan 100 pounds. Microwave waveguide 22 propagates power from microwavepower source 12. Plasma 42 is induced by waveguide 22 which ispenetrated by openings in the walls of waveguide 22 such that plasma gasflows transverse to the direction of microwave power propagation 20 inwaveguide 22. In a preferred embodiment, waveguide 22 includes shortedend 26 and tapers 24a, 24b where the plasma is induced from the designof waveguide 22. Tapers 24a, 24b intensify the electric field andfacilitate plasma breakdown.

Waveguide 22 may also include impedance matching waveguide section 28,which provides maximum transfer of energy from microwave power source 12through waveguide 22 to plasma 42 by minimizing reflection. The openingsin the waveguide walls are smaller than one quarter of the microwavewavelength and the gas flow passage through waveguide 22 is preferablylined with dielectric material or liner 30 which is transparent to themicrowaves. While not meant to be limiting, dielectric materials such asboron nitride or fused quartz are suitable for use in the presentinvention.

The portable trace element sensor devices in accordance with the presentinvention utilize a high-power microwave plasma for atomic emissionspectroscopy of solid, liquid or gas samples that are entrained in thegas flow through the plasma. In contrast to present microwave plasmaspectrometer systems used in laboratories, the portable microwave plasmatrack element sensor of the present invention can use a pulsed orcontinuous microwave source. The use of pulsed operation allows thedevice to achieve high peak powers without the larger power supplyrequirements of a continuous power supply. The combination of pulselengths and pulse repetition rates may be such that a low average powersupply may be used (1 to 100 watts) in order to keep the device compactand portable. Alternatively, the microwave source may operate in anon-pulsed mode with a higher capacity power supply system.

As further illustrated in FIG. 1, microwave power source 12 includesforward power detector 14 and reflected power detector 16. Microwavepower source 12 may be a magnetron or the like. One class of microwavesources, such as magnetrons used in typical kitchen microwave ovens andthe like, may achieve peak powers of about 200 to 2000 watts withaverage pulse lengths in the 0.01 to 1 second range. The pulserepetition rate may be one pulse per second or longer. Another class ofmicrowave sources, such as those used in radar, may achieve peak powersreaching 10⁶ watts with pulse lengths on the order of approximately 10⁻⁶seconds. The pulse repetition rate in this case may be up to about 100per second. In either embodiment, the average power requirement may berelatively low, i.e. in the 1-100 watt range. In a preferred embodiment,microwave power source 12 is connected to portable power supply 70having filament 62 and anode 64 connections. Reflected power dump 18 isconnected to circulator 58 as illustrated in FIG. 1. Portable powersupply 70 is connected to computer 60, which preferably is connected toportable battery charger 80. Portable power supply 70 is also connectedto exhaust pump 40 as shown in FIG. 1.

The portable unit may also be operated with a microwave, tube filamentthat is continuously on (to reduce wear) while the main microwave powersource operation is in a pulsed mode. It may also be desirable to usecontinuous microwave tube operation; however, the operator would thenhave to transport a larger power supply unit at all times.

Exhaust pump 40 or compressed gas 38 may be used to establish entrainedsample flow through plasma 42 of waveguide 22. Samples may be introducedinto plasma gas flow 42 as liquid through liquid sample input 46 andnebulizer 34 as shown in FIG. 1. Alternatively, samples may beintroduced into plasma gas flow 42 as solid particulates which can beplaced on the end of a graphite dielectric rod subsystem 50 or the likeand inserted into plasma flame 42 through dielectric tube 32 which isproximate to the base of flame 42. While not meant to be limiting,alumina or other ceramic tubes topped with a spectrographic graphite rodare suitable for use as sample rods according to the present invention.In yet another alternative embodiment of the invention, samples may beintroduced into plasma gas flow 42 as gas via gas sample input 48.Samples which have passed through plasma 42 exit device 10 as exhaust52, and may subsequently be treated using appropriate measures.

Solid sample quantities of less than about one milligram would besufficient for analysis. If a solid sample requires size reduction, asmall hand held size reduction device can be utilized to reduce the sizeof the particles. For example, solid samples can be reduced toparticulates by a simple hand carried grinder prior to inspection in themicrowave plasma device. If the solid sample is in the correct particlesize range, the sample may be analyzed directly.

An electrical starting circuit incorporated into the present inventionfacilitates reproducible restart of the microwave plasma with eachpulse. As shown in FIG. 1, high voltage starter 44 is incorporated intodevice 10 in order to produce a spark or corona to reproducibly restartthe plasma during pulsed operation with microwave power levels that aretoo low to initiate a plasma breakdown, i.e., less than about 10 kW.Starter 44 may be a Telsa coil, an automotive ignition coil or the like.The entry of the starter graphite plasma arc into device 10 is wellinsulated using insulator 36 or the like so that sparking occurs at thetip nearest the base of plasma 42. A grounded wire point may bepositioned near plasma arc starter to facilitate sparking. Starter 44may be connected to, portable power supply 70.

As a sample passes through plasma 42, fiber optic guides 54 transmit theplasma light to spectrometer system 56 (such as a Czerny Turner gratingconfiguration) which identifies the element or elements present in theplasma gas flow by the line spectra of the respective element orelements present in the sample. The fiber optic guides penetrate throughthe dielectric liner 30 so their light collection efficiency ismaximized and their ends are exposed to the plasma flame heat and gasflow to keep them clean. Multiple fibers and spectrometers may beemployed to monitor as many elements as needed simultaneously forcharacterization of a particular site. Simple interference filters witha single detector per element may also be used to simplify the lightanalysis in certain applications and to facilitate a more compactdesign.

Portable computer 60, preferably with its own rechargeable battery pack,may control spectrometer system 56, monitor detectors 14, 16, anddisplay the spectra. Portable computer 60 may also be programmed toprovide a compositional analysis of the sample being studied. Computer60 may further be utilized to control the operation of microwave source12 through a connection to portable power supply 70.

As discussed herein, portable power supply 70 for powering microwavesource 12, starter 44, and exhaust pump 40 preferably utilizesrechargeable batteries with appropriate electronics to provide theproper voltages to the various subsystems of portable element sensordevice 10. A portable battery charger 80 may be utilized to rechargecomputer 60 and portable power supply batteries as needed. Exemplaryembodiments of the portable power supply 70 and charger 80 will be nowbe discussed.

Referring now to FIG. 2, a portable power supply circuit 70 that issuitable for use in accordance with the present invention is shown. Thepower supply that is used in accordance with present invention iscompact and is capable of employing a different source of electricity incontrast to electricity from a wall plug as is used by current devices.In addition, the associated battery charger 80 (see FIG. 3) provides acompact source of energy.

For purposes of illustration, portable power supply 70 in FIG. 2 depictsa magnetron microwave source which utilizes a low voltage, high currentfilament supply and a high voltage, lower current anode supply. Thevoltage/current parameters used are appropriate for a magnetron tubethat is commonly used in conventional microwave ovens in kitchens. Itshould be appreciated, however, that other microwave sources aresuitable for use in the present invention. Such a tube may be readilyadapted for use in connection with the portable trace element sensordevice of the present invention. This type of power supply also usesrelatively light weight, rechargeable nickel-cadmium, metal hydride orlithium batteries.

Preferably, power supply circuit 70 is capable of delivering 4000 voltsDC at 200 milliamperes for one-second intervals repeatedly at minimumintervals of 30 seconds to magnetron anode 64. Under these conditions, afully charged battery 162 preferably provides at least about 300 testsprior to discharge. In one embodiment, battery 162 is a 24 volt batterycapable of being fully recharged in about 6 hours at a rate of 6amperes. Batteries 102 and 190 are also preferably designed so as to becapable of being recharged simultaneously with battery 162 using thesame battery charger (such as the type of battery charger 80 as shown inFIG. 3).

Battery power sources 102, 162 and 190 preferably are mounted in thesame enclosure and designed so that a fully charged spare battery setmay be readily connected to power the portable trace element sensor 10.As illustrated in FIG. 2, battery 102 supplies power through switch 100to the square wave oscillator circuit 115. In one embodiment of theinvention, oscillator circuit 115 comprises an oscillator integratedcircuit chip 104, such as a 555, connected to resistors 106, 108 andcapacitors 110, 112 which determine the interval and period for thegenerated square wave.

The signal generated by oscillator 115 is fed through isolationtransformer 118 whose outputs are connected through diodes 120 and 122and resistors 124 and 126 for rectification and isolation. Resistors 124and 126 are further connected to resistors 128 and 130 prior toconnection to zener diodes 132 and 134. Zener diodes 132 and 134regulate the voltage levels fed into the next amplification stage.

The voltage waveforms found on zener diodes 132 and 134 are fed toHEXFETS 136 and 138 respectively. HEXFETS 136 and 138 amplify the signaland are utilized to drive step-up transformer 140. The output of step-uptransformer 140 is further connected through an isolation rectificationcircuit comprising diodes 142 and 144 with resistors 146, 148, as foundconnected to the output of transformer 118. The signals thus generatedare used to drive HEXFETS 166, 168, 170, and 172 through resistors 150,152, 154 and 156, respectively. The 30 kilohertz square wave is suppliedthrough transformer 118 to the gates of HEXFETS 136 and 138 which inturn power the gates of HEXFETS 156, 168, 170 and 172. It should beappreciated that while FIG. 2 illustrates two HEXFETS in parallel, threeor four HEXFETS may be used in parallel to conserve power from battery162. Using an intermediate set of HEXFETS (136 and 138) to drive thehigher power HEXFETS (166, 168, 170 and 172) facilitates a moreefficient power supply design. HEXFETS, 166, 168, 170 and 172 areutilized to drive the final transformer 174.

Battery 162 provides a source of energy for the anode 64. For example,energy from battery 162 may be converted to about 4000 DC for the anode64. Switch 164 provides a control for turning the anode on and off.While not intending to be limiting, switch 164 can be controlled bycomputer 60.

Final transformer 174 is connected through diode chains 176 and 178, tocapacitors 180 and 182 and resistors 184 and 186 respectively, whichrectify and smooth the voltage waveform outputted by transformer 174.The power supply voltage is then presented to connector 188 for supplyto the microwave generator.

Transformer 174 is a high frequency, high voltage power transformerwhich is preferably both compact and light weight. The input is theHEXFET (166, 168, 170, 172) switched 24 volts from battery 162 and isstepped up to 2000 volts, square wave by transformer 174 which operatesat 30 kilohertz.

In one embodiment of the invention, diodes 176 and 178 each include five1000 volt, 2.5 amperes diodes connected in series. Capacitors 180 and182 are each rated at least 3000 volts DC and have a capacitance of 0.1microfarad. Resistors 184 and 186 are each 20 megaohms 1 watt and willdischarge capacitors 180 and 182 in less than 10 seconds after power isshut off. The circuit which includes the secondary winding oftransformer 174, diodes 176 and 178, and capacitors 180 and 182 is aconventional voltage doubling circuit. It will be appreciated by thoseskilled in the art, however, that the particular embodiments of theinvention described are shown by way of illustration and not aslimitations of the invention. The principle features of this inventioncan be employed in various embodiments without departing from the scopeof the invention. For example, diodes 176 and 178 can each include a5000 volt diode rather than five 1000 volt diodes.

The 3.3 volt, 10 amperes filament power 194 for magnetron 12 can beprovided in the most efficient manner utilizing a series-parallelconnection of 9 size D industrial type nickel-cadmium batteries.

The operation of the power supply circuit 70 will now be described.Switch 192 is closed first for at least one minute in order to properlyheat magnetron filament 194 and obtain several analyses of the materialbeing tested. If the magnetron filament current is not manually turnedoff in approximately three minutes, an automatic timing circuit willshut off filament power and prevent undesirable discharge of thebatteries. Alternatively, if the batteries are sufficiently robust, thefilament can be left on for all sample pulses to increase filament lifetime. Switch 100 is closed next, thereby initiating oscillatorintegrated circuit chip 104 and providing 30 kilohertz square wavepulses to all of the HEXFETS gates. The magnetron anode power 188 isturned on by closing switch 164 which in turn starts a one-second timer.At the end of the one second, anode power is turned off. By openingswitch 164 and waiting for at least 30 seconds, the anode circuit may bereenergized by closing switch 164 and analyzing another sample.

Referring now to FIG. 3, a simple, light weight portable batterycharging system 80 which includes a small, light weight gasoline enginegenerator 200. An engine capable of generating about one kilowatt issuitable for use in accordance with the present invention. For example,internal combustion engines such as the those used with a "WEEDWACKER"™, a leaf blower or a chain saw are suitable for use. The engineis directly connected to a small alternator 202. Alternators of the typeused in a motorcycle, a small automobile or the like are suitable foruse in accordance with the present invention. Alternator 202 may be asingle, two-phase or three-phase alternator. The alternator stator maybe rewound to provide three separate windings with an appropriatelysized full wave bridge rectifier connected to each winding, therebyproviding the proper voltage for charging batteries 102, 162 and 190 andthe computer battery pack. The device car be powered primarily with thebatteries. Alternatively, the device can be powered using the batteriesfor peak power during pulsing. This can be accomplished by providing anengine 200 and an alternator 202 of sufficient size and capability thatthe device can be operated in a continuous mode without reducing theampere-hour capacity or energy storage capacity of the batteries (whenthe batteries are used alone).

It is also possible to rewind the alternator stator for single-phase ortwo-phase operation and then use a transformer such as transformer 204shown in FIG. 3 to provide the proper DC voltage for each of the fourbatteries. Transformer 204 is preferably a small higher frequencytransformer. In one embodiment of the invention, inductors 206, 208 and210 may be employed to limit DC current and improve battery chargingcharacteristics. In this embodiment, rectifiers 212, 214 and 216 areconnected to inductors 206, 208 and 210, respectively. Rectifiers 212,214 and 216 are connected to batteries 102, 162 and 190, respectively.

The features of the portable microwave plasma torch element sensordevice 10 described above allow the plasma torch to be portable andcompact, i.e., on the order of the size of the waveguide. In thismanner, the device may be transported from site to site by an individualwithout the need for heavy or large equipment. FIG. 4 is an exemplaryillustration of the compact and portable features of the invention. Themodular arrangement illustrated in FIG. 4 contains three modules 220,230 and 240. Module 220 contains the plasma torch with the opticalsensor in addition to the computer. As further shown in FIG. 4, module230 contains power supply circuit 70 and module 240 contains batterycharger 80. The modules are connected by cables 242, 244 and 246. Cablesuch as coaxial cable is suitable for use in accordance with the presentinvention. It will be appreciated by those skilled in the art that themodular arrangement shown in FIG. 4 is exemplary and can be modified inaccordance with the present invention. The modular arrangementfacilitates,transportation and ease of operation of the device. Forexample, transportation of a plurality of modules (using a dolly or thelike) allows the device to be readily transported through airports, toand from field sites, and the like. Ease of operation is facilitatedwith the use of the cables to connect the modules at a particular site.In some instances, it may be desirable to adjust the cable lengths suchthat one or more modules can be placed in close proximity to the sampleto be analyzed while the other module or modules are placed a furtherdistance from the sample to be analyzed. For example, space restrictionsmay make it desirable to take, a module containing the plasma torch withthe optical sensor into a mine shaft while leaving the other module ormodules at the earth's surface. The modules can be connected by thecables so that samples can be analyzed as previously described.

In addition, the sensor device of the present invention provides aplasma torch which is safe from microwave leakage to the operator. Thiscan be attributed at least in part to the waveguide openings being smallrelative to the wavelength. Moreover, the portable sensor deviceprovides a plasma torch which is robust as a result of the microwavepower density being maximized by tapering of the waveguide.

The compact portable microwave plasma torch system of the presentinvention provides distinct advantages over the prior art. It differssignificantly from relatively large microwave induced plasma systemsused in the laboratory. See e.g., Zander et al., Microwave-SupportedDischarges, Applied Spectroscopy, Vol. 35, p. 357 (1981); Forbes, etal., Comparison of Microwave-Induced Plasma Sources, Journal of AnalyticAtomic Spectrometry, Vol. 6, p. 57 (1991), both of which areincorporated herein by reference. It also differs significantly from infurnace off gas analysis applications.

Another advantage associated with the present invention will be theability to accept samples for analysis without special preparation,regardless of whether the sample is in a solid, liquid or gas state.Existing laboratory units are generally designed to accept only one ofthese states in a specially prepared matrix.

It should be appreciated by those skilled in the art that the specificembodiments disclosed above may readily be utilized as a basis formodifying or designing other methods or structures for carrying out thesame purpose of the present invention. It should also be realized bythose skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

What is claimed is:
 1. A method for analyzing a gas, liquid or solidsample, comprising:establishing a plasma in a portable waveguide exposedto the gas, liquid or solid sample; transmitting emitted plasma light toa spectrometer; dispersing the emitted light with said spectrometer;detecting the dispersed light with a detector; and analyzing thedetected light with a computer to determine the elementalcomposition,wherein the means for establishing comprise a portable powersupply.
 2. The method of claim 1, wherein the sample is a liquid andwherein the method further comprises introducing the liquid samplethrough a nebulizer into the waveguide for flow through the plasma. 3.The method of claim 2, wherein the step of introducing includes usingcompressed gas to establish flow of the sample through the plasma.
 4. Amethod for analyzing a solid sample, comprising:establishing a plasma ina portable waveguide; placing the solid sample on a dielectric rod;inserting the rod and the sample into the plasma; transmitting emittedplasma light to a spectrometer; dispersing the emitted light with saidspectrometer; detecting the dispersed light with a detector; andanalyzing the detected light with a computer to determine the elementalcomposition,wherein the means for establishing comprise a portable powersupply.
 5. The method of claim 4, wherein the dielectric rod has agraphite sample receptacle.
 6. The method of claim 5, wherein the stepof inserting includes inserting the dielectric rod and the samplethrough a dielectric tube.
 7. The method of claim 6, wherein an end ofthe dielectric tube is proximate to the base of the plasma.
 8. Themethod of claim 4, wherein the step of inserting includes inserting thedielectric rod and the sample through a dielectric tube.
 9. The methodof claim 8, wherein an end of the dielectric tube is proximate to thebase of the plasma.